View full sizeUNIVERSAL PICTURESHarrison Ford, left, and Daniel Craig are shown in a scene from "Cowboys & Aliens."

LOS ANGELES — Little blue Smurfs and not-so-little green men from space are in a photo finish for the No. 1 spot at the weekend box office.

Daniel Craig and Harrison Ford’s sci-fi Western “Cowboys & Aliens” and the family adventure “The Smurfs” both opened with $36.2 million, according to studio estimates Sunday.

That leaves Sony’s “Smurfs” and Universal’s “Cowboys & Aliens” tied for the top spot. Figuring out the No. 1 movie will have to wait until final numbers are counted Monday.

“In all my years, I’ve never really seen a race this close,” said Paul Dergarabedian, an analyst for box-office tracker Hollywood.com. “Generally, in the world of movie box office, $1 million is a close call, so to have two films in a dollar-to-dollar tie is somewhat unprecedented.”

Studios often round off their Sunday numbers, which include Friday and Saturday totals plus an estimate of Sunday business based on how similar movies have done in the past.

So Sunday figures typically are rounded off to the nearest $50,000 or $100,000, with more accurate, to-the-dollar numbers generally coming in Monday’s final tally.

But Universal released an estimate of $36,206,250, which would have put “Cowboys & Aliens” a fraction ahead of “The Smurfs” in Sunday’s rankings. So Sony, which had reported a rounded-off figure of $36.2 million, matched that $36,206,250 estimate for “The Smurfs.”

“We’re going with that extra $6,250, because it’s just too close to call,” said Rory Bruer, head of distribution at Sony. “It just seems like the most fair thing to do is call it a tie and let Monday sort it out.”

Studios jockey for the top box-office spot to earn “No. 1 film in America” bragging rights in advertising for the coming week.

Going into the weekend, “Cowboys & Aliens” seemed to have the edge, with analysts figuring it might top $40 million, while “The Smurfs” might come in around $30 million.

But the two movies met in the middle, “Cowboys & Aliens” doing worse than expected and “The Smurfs” doing better.

“This is truly a photo finish,” said Nikki Rocco, head of distribution for Universal. “Nobody can call it. The truth of the matter is, it’s a tie, and with two totally different kinds of films.”

“Cowboys & Aliens” stars Craig as an amnesiac wanderer who teams with cattle baron Ford to take on hulking aliens that invade a town in the Old West. “The Smurfs” brings the blue cartoon creatures to the big screen, with a voice and live-action cast that includes Katy Perry, Hank Azaria, George Lopez and Neil Patrick Harris.

Because it opened in fewer theaters, “The Smurfs” did more business on average at cinemas. Playing in 3,395 locations, “The Smurfs” averaged $10,665 a theater, compared to a $9,655 average in 3,750 cinemas for “Cowboys & Aliens.”

“The Smurfs” had a ticket-price advantage with 3-D screenings, which cost a few dollars more and accounted for 45 percent of business. But 25 percent of its business came from children under 12, who get in at discount prices, while “Cowboys & Aliens” drew adult crowds paying full admission.

So it’s tough to determine which movie actually sold more tickets.

The weekend’s other new wide release, the Warner Bros. romantic comedy “Crazy, Stupid, Love,” opened modestly at No. 5 with $19.3 million. The movie stars Steve Carell as a one-woman man who learns the art of seduction from a playboy (Ryan Gosling) after his marriage falls apart.

The previous weekend’s top movie, “Captain America: The First Avenger,” slipped to No. 3 with $24.9 million and raised its domestic total to $116.8 million.

“Harry Potter and the Deathly Hallows: Part 2” pulled in $21.9 million to become the franchise’s top-grossing chapter at $318.5 million domestically.

That tops the previous high of $317.6 million for the 2001 original, “Harry Potter and the Sorcerer’s Stone.” But factoring in today’s higher ticket prices, “Deathly Hallows: Part 2” so far has sold fewer tickets than “Sorcerer’s Stone.”

Also this weekend, the “Harry Potter” finale became the first of the franchise’s eight movies to top $1 billion at the box office worldwide.